class_docstr: Event system that handles storing and calling callbacks for events.
  
  Attributes:
      callback_map (Dict[str, List[Callable]]) : Stores list of callbacks
          for events when registered.
code: def __init__(self):
      self.callback_map = {}
  
file_path: ray/python/ray/autoscaler/_private/event_system.py
imports: from enum import Enum, auto
  from typing import Any, Callable, Dict, List, Optional, Union
  from ray.autoscaler._private.cli_logger import cli_logger
label_desc: Use image node_id 1 to create a new _EventSystem object  with example: obj = _EventSystem()